Generics & ArrayList

Question 1

An ArrayList is less efficient than an array.

Answer 1

True.

Question 2

ArrayList’s use the same bracket notation as arrays.

Answer 2

False.

Question 3

The base type of an ArrayList cannot be a primitive type.

Answer 3

True.

Question 4

The base type of an ArrayList can be an integer.

Answer 4

True.

Question 5

The ArrayList class is built into what java package?

Answer 5

java.util

Question 6

You can specify the initial capacity of an ArrayList.

Answer 6

True.

Question 7

Specifying an initial capacity limits the size to which an ArrayList can grow.

Answer 7

False.

Question 8

The following is a valid syntax for the 2-parameter .add() method:
list.add(2, Object1);

Answer 8

True.

Question 9

When you specify the index in .add(), the element originally at that index is replaced.

Answer 9

False (it and the those that follow are shifted up the list).

Question 10

What is the name of the method that returns the number of elements in an ArrayList?

Answer 10

list.size();

Question 11

What ArrayList method is used to replace elements at a specific index?

Answer 11

.set(index, object1);

Question 12

list.add(5, object1) is valid if list has 4 elements.

Answer 12

False, but list.add(4, object1) is valid.

Question 13

list.set(4, object1) is valid if list has 4 elements.

Answer 13

False, set() can only reset an element at an index that already contains an element.

Question 14

A call to the ArrayList’s default constructor creates an empty ArrayList with what initial capacity?

Answer 14

10.

Question 15

remove(int index) returns the Object removed.

Answer 15

True.

Question 16

list.removeRange(3, 7); removes the elements from indices 3 up to and including the element at index 7.

Answer 16

False, the element at index 7 is not removed.

Question 17

list.trimToSize(6); trims an list to only 6 elements.

Answer 17

False, trimToSize() does not take any arguments.

Question 18

If list is an ArrayList of base type String, then the following is valid:
String[] list2 = list.toArray();

Answer 18

False, .toArray() returns an array of type Object. Correction:
String[] list2 = (String[]) list.toArray();

Question 19

If list is an ArrayList of type String, and list2 if of type String[], then the following always copies list into list2:
list.toArray(list2);

Answer 19

False, if list2 isn’t big enough to hold all elements in list, then the operation fails.

Question 20

If list is an ArrayList of base type String and list2 if of type String[], then the following always copies list into list2:
list2 = list.toArray(list2);

Answer 20

True, unless list2 is null (run-time error) or not initialized (compiler error) - then the code fails.

Question 21

If list is an ArrayList of base type String and has length 3, and list2 if of type String[] and has length 6, what happens to indices 3 - 5 of list2?
list.toArray(list2);

Answer 21

They remain as they were previously defined.

Question 22

If list is an ArrayList of base type String with 3 elements, then the following will run:
foreach (String x : list) {System.out.println(x);}

Answer 22

False (replace foreach with for).

Question 23

If list is an ArrayList of base type String, with 3 elements, then the following will run:
for (list : String x) {System.out.println(x);}

Answer 23

False (swap ‘list’ and ‘String x’).

Question 24

The following syntax works for iterating over LinkedLists as well as ArrayLists:
for (Type x : list) {…}

Answer 24

True.

Question 25

In memory, ArrayLists grow and shrink automatically.

Answer 25

False, ArrayLists do not shrink automatically - shrinking requires an invocation of trimToSize().

Question 26

It is always possible to make a deep copy of an ArrayList.

Answer 26

False - not if it is impossible to make a deep copy of objects of the base type.

Question 27

The following is a valid line:
ArrayList list = new ArrayList();

Answer 27

True - there exists an ArrayList class with no type parameter (of base type Object).

Question 28

Any non-keyword identifier can be used for the type parameter in a class definition.

Answer 28

True - T is only used by convention.

Question 29

The following is a valid instantiation of the generic class “Thing”:
Thing<String> = new Thing();</String>

Answer 29

False, correction:
Thing<String> = new Thing<String>();</String></String>

Question 30

The following is a valid definition the generic Thing class default constructor:
public Thing() { attribute = null; }

Answer 30

True - you must not put the type parameter in the constructor headings, unless it is to define the type of a parameter.

Question 31

Arrays are valid reference types that can be plugged in for a type parameter.

Answer 31

True.

Question 32

If list is an ArrayList of type integer, then the following is valid.
list.add(1);

Answer 32

True (automatic boxing).

Question 33

Class definitions can only have a limited number of type parameters.

Answer 33

False.

Question 34

A generic class can be an exception class.

Answer 34

False, a generic class cannot extend any descendent class of Throwable.

Question 35

Write the class header for a generic class named “C1” which only accepts instances or children of class “C2” for its type parameter.

Answer 35

public class C1 < T extends C2 > {…}

Question 36

Write the class header for a generic class named “C1” which only accepts classes that implement interface “I1” as their type parameter.

Answer 36

public class C1 < T extends I1 > {…}

Question 37

The following is a valid class header:
public class C<T1 extends A, T2 extends A & A2> {…}

Answer 37

True.

Question 38

Interfaces can be made generic (made to accept type parameters).

Answer 38

True.

Question 39

Generic methods can be defined, whose type parameter does not belong to any class.

Answer 39

True.

Question 40

Generic methods can only be written in generic classes.

Answer 40

False.

Question 41

The type parameter of a generic method becomes local to the class, if the class itself is generic.

Answer 41

False - the type parameter of a generic method is local to that method.

Question 42

The following is a valid signature for a generic method:
public static T genMethod(T[] a)<T> {...}</T>

Answer 42

False - the type parameter must come after all the modifiers, and before the return type:
public static <T> T genMethod(T[] a) {...}</T>

Question 43

The following is a valid invocation of a generic method:
String s = NonG.< String >genMethod(c);

Answer 43

True.

Question 44

Generic classes can be defined as a derived class of another generic class or of an ordinary class.

Answer 44

True.

Question 45

If B is a subclass of A, and G is a generic class, then G< A > is a superclass of G< B >.

Answer 45

False, there is no relationship between G< A > and G< B >, no matter the relationship between A and B.

Question 46

The following is a valid use of the type parameter:
T object = new T();

Answer 46

False. The type parameter cannot be used in expressions involving “new”.

Question 47

The following is a valid use of the type parameter:
Pair< String >[] a = new Pair< String >[10];

Answer 47

False, you cannot create arrays of generics.

Question 48

The following is a valid use of the type parameter:
T[] a = new T[10];

Answer 48

False.

Question 49

Why can’t you create arrays of generics?

Answer 49

By design, Java requires arrays at run-time to include information about their contents.

Question 50

The following is a valid use of the type parameter:
Pair<String[]> a = new Pair<String[]>();

Answer 50

True.

Question 51

The following is a valid use of the type parameter:
Pair<Pair<String[]» a =
new Pair<Pair<String[]»();

Answer 51

True.